Several bisphosphonates are now available for the treatment of osteoporosis. Porous hydroxyapatite/collagen (HA/Col) composite is an osteoconductive bone substitute which is resorbed by osteoclasts. The effects of the bisphosphonate alendronate on the formation of bone in porous HA/Col and its resorption by osteoclasts were evaluated using a rabbit model. Porous HA/Col cylinders measuring 6 mm in diameter and 8 mm in length, with a pore size of 100 μm to 500 μm and 95% porosity, were inserted into a defect produced in the lateral femoral condyles of 72 rabbits. The rabbits were divided into four groups based on the protocol of alendronate administration: the control group did not receive any alendronate, the pre group had alendronate treatment for three weeks prior to the implantation of the HA/Col, the post group had alendronate treatment following implantation until euthanasia, and the pre+post group had continuous alendronate treatment from three weeks prior to surgery until euthanasia. All rabbits were injected intravenously with either saline or alendronate (7.5 μg/kg) once a week. Each group had 18 rabbits, six in each group being killed at three, six and 12 weeks post-operatively. Alendronate administration suppressed the resorption of the implants. Additionally, the mineral densities of newly formed bone in the alendronate-treated groups were lower than those in the control group at 12 weeks post-operatively. Interestingly, the number of osteoclasts attached to the implant correlated with the extent of bone formation at three weeks.

In conclusion, the systemic administration of alendronate in our rabbit model at a dose-for-weight equivalent to the clinical dose used in the treatment of osteoporosis in Japan affected the mineral density and remodelling of bone tissue in implanted porous HA/Col composites.

We have managed 21 patients with a fracture of the tibia complicated by bone and soft-tissue loss as a result of an open fracture in 10, or following debridement of an infected nonunion in 11, by resection of all the devitalised tissues, acute limb shortening to close the defect, application of an external fixator and metaphyseal osteotomy for re-lengthening. The mean bone loss was 4.7 cm (3 to 11). The mean age of the patients was 28.8 years (12 to 54) and the mean follow-up was 34.8 months (24 to 75).

All the fractures united with a well-aligned limb. The mean duration of treatment for the ten grade-III A+B open fractures (according to the Gustilo-Anderson classification) was 5.7 months (4.5 to 8) and for the nonunions, 7.6 months (5.5 to 12.5). Complications included one refracture, one transient palsy of the peroneal nerve and one equinus contracture of 10°.